J/AN/321/81 Orion Trapezium area ROSAT PSPC obs. II. (Lohother/mann+, 2000)
ROSAT PSPC observations of the Orion Trapezium area.
II. Source variability and revised source list.
Lohmann P., Wendker H.J.
<Astron. Nachrichten, 321, 81 (2000)>
=2000AN....321...81L 2000AN....321...81L
ADC_Keywords: Clusters, open ; X-ray sources ; Stars, pre-main sequence
Mission_Name: ROSAT
Keywords: open clusters and associations: general -
open clusters and associations: individual (Orion OB1) -
stars: activity - stars: pre-main sequence - X-rays
Abstract:
A deep ROSAT PSPC image centred on the Orion Trapezium has been
reduced a second time using an improved version of the PSF to fit the
data. The outer rim of the field of view was also included. The new
catalogue contains 316 X-ray sources which are easily identified with
pre-main sequence stars of the Ori OB1 Ic and Id association. All 316
sources were tested for variability. No variations were found inside
the single exposures of about 45 minutes length each. Between the 4
exposures spaced over 5 days about 1/3 of the sources show signs of
activities of various forms. As above 25% of these have somewhat
regular lights curves (monotonically rising or falling or hill-
shaped) we infer that at least some outbursts with time scales longer
than a day are present and that past searches for X-ray flares of
pre-main sequence stars were biased towards shorter time scales.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 96 316 Properties of ROSAT PSPC X-ray sources in the
Orion Trapezium area
notes.dat 80 239 Remarks on individual sources (table2)
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See also:
IX/30 : Second ROSAT PSPC Catalog (ROSAT, 2000)
IX/31 : The WGACAT version of ROSAT sources (White+ 2000)
IX/32 : ROSAT Bright Survey (Fischer+, 1998-2000)
J/A+A/299/39 : Orion Trapezium area ROSAT PSPC obs. I. (Geier+, 1995)
J/ApJ/540/1016 : K-band & NICMOS phot. of Trapezium Cluster (Luhman+, 2000)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ROS-ORI [1/316]+ Sequential number (1)
4 A1 --- n_ROS-ORI [*] indicates a note in notes.dat file
5- 6 I2 h RAh Right ascension (J2000.0)
8- 9 I2 min RAm Right ascension (J2000.0)
11- 14 F4.1 s RAs Right ascension (J2000.0)
16 A1 --- DE- Declination sign (J2000.0)
17- 18 I2 deg DEd Declination (J2000.0)
20- 21 I2 arcmin DEm Declination (J2000.0)
23- 24 I2 arcsec DEs Declination (J2000.0)
26- 30 F5.2 arcmin phi Off-axis angle
32- 38 F7.2 ct/ks eta Source count rate
40- 44 F5.1 --- S/N Signal to noise ratio
46- 50 F5.1 arcsec RX Apparent source radius (2)
52- 56 F5.2 --- HR2 Hardness ratio HR2 (3)
58- 61 F4.2 --- e_HR2 rms uncertainty on HR2
63 A1 --- Var [PV] Variablity type (4)
65-104 A40 --- Rem Remarks (5)
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Note (1): No. 1 to 171 are the same as in paper I, J/A+A/299/39
Note (2): Radius of the circle around a nominal source centre where the PSF
dropped to 20% of its maximum value
Note (3): HR2 = [n(41-100) - n(101-240)]/[n(41-100) + n(101-240)],
where n(a-b) is the number n of photons in channel numbers a to b.
Note (4): Source variability:
" " not variable
"V" variable, the variability indicator ζ is ζ>P
"P" probably variable, ζ between 3 and 4
Note (5): Optical identifications and an indication of when source parameters
were derived in the hard band (energy channels 41 to 201) only
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Byte-by-byte Description of file: notes.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ROS-ORI Sequential number
5- 80 A76 --- Rem Text of the remark
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History:
Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 05-Oct-2000